When holding a telescopic optical instrument, as typified by a monocular device or binoculars, with hands, and operating it to make observations of an object and, in particular, when operating a hand-held telescopic optical instrument in a flying aircraft or a moving vehicle, the instrument encounters hand-shakings arising from vibrations (oscillating angular displacements or motions of the longitudinal axis of an aircraft or a vehicle due to yawing and pitching) of the flying aircraft or the moving vehicle imparted to a housing of the optical instrument. Such the hand-shakings cause the telescopic optical instrument to develop fluctuations in the angle of a beam of light emanating from the object under observation relative to an optical axis of the optical system of the optical instrument (which is hereinafter referred to as the “telescopic optical system”), resulting in deteriorations in the quality of an optical image of the object under observation. These deteriorations may include at least blurring of the telescopic optical image, or image-shakings (shakings of an image responding to hand-shakings which means vibrations of the hand-held telescopic optical instrument), and aggravation of resolution of the optical images, among others. Even if vibrations imparted or applied to the optical instrument are small in amplitude, measurable deteriorations are induced in the quality of an optical image of an object under observation because that the optical instrument, in the case of monocular or binocular devices, has only a narrow field of view and that an image formed by an objective lens is magnified through an eyepiece lens.
Conventionally, there has been proposed various optical image stabilizers to compensate for deteriorations in the quality of a telescopic optical image of an object under observation due to hand-shakings.
An example of optical image stabilizers of conventional telescopic optical instruments with a function of compensating for image-shakings is disclosed in the publication of published Japanese application No. 57-(1982)37852 (which corresponds to U.S. Pat. No. 4,235,506 now expired and is hereinafter referred to as Document I). This optical image stabilizer, which is of the form incorporated in binoculars having a pair of right and left telescopic optical systems, comprises a pair of right and left erect prisms each of which is disposed between an objective lens and an eyepiece lens of each telescopic optical system of the binoculars, a single prism holder frame for fixedly holding the right and left erect prisms, a gimbal device disposed axially between the pair of objective lenses and the pair of eyepiece lenses for suspending the prism holder frame for rotation about two axes orthogonally intersecting with each other in a plane perpendicular to optical axes of the telescopic optical systems, and a single gyro motor fixedly attached to the gimbal device.
The optical image stabilizer is functional in that a driving mechanism for the gimbal device can be rendered structurally simple by virtue of such constitution that the single gyro motor drives the gimbal device suspending the single prism holder frame with the pair of right and left erect prisms fixedly held thereby.
Incidentally, when dealing with lateral or horizontal vibrations of the binoculars (oscillating angular displacements or motions of the longitudinal axis of the binoculars due to yawing), the conventional optical image stabilizer installed in the binoculars disclosed in Document I causes rotation of the prism holder frame about one of two orthogonally intersecting axes of rotation, namely the vertical axis of ration, centrally located at a point of intersection between the right and the left telescopic optical system. In this instance, the erect prism of, for example, the left telescopic optical system is displaced in axial position toward the object side lens and the erect prism of the right telescopic optical system is displaced in axial position toward the image side, so that the distance between the erect prism and the objective lens becomes different between the right and the left telescopic optical system. This results in that the telescopic optical image becomes different in visual appearance between the right and the left optical systems. In other words, the optical image stabilizer of Document I has the result that, as the respective telescopic optical systems are rendered disconformable in physical relationship among their optical components when the optical image stabilizer reacts to deal with horizontal vibrations or motions, telescopic optical images respectively viewed through the telescopic optical systems are visually differently from each other.
Another image stabilizing optical device for a telescope, which is disclosed in published Japanese application No. 6(1994)-250100 (which is hereinafter referred to as Document II) is structurally similar to that of Document I with the exception that a gimbal device with a pair of right and left erect prisms retained by a single prism holder frame is servo-controlled to rotate and return to a specified state or an initial state so as thereby to compensate for deteriorations of a telescopic optical image, such as image-shakings, responding to vibrations imparted to the optical instrument. This angular velocity detection means mounted on the prism holder frame detects in the form of information on a rotational angle of the gimbal device relative to an inertial space arising due to the vibrations. As this optical image stabilizer is provided, in place of a gyro motor for a gimbal actuator, with a drive mechanism which comprises a rotary motor for rotating pivot shafts of the gimbal device and position detector means such as a potentiometer for detecting an angle of rotation of the gimbal device, the optical image stabilizer is ensured to be miniaturized, weight-saved, and need little electricity to work.
At the same time, although the optical image stabilizer disclosed in Document II has an effect on miniaturizing the telescopic optical systems of the binoculars which has a pair of erect prisms, nevertheless, since the rotary motor for rotating gimbal shafts and the potentiometer need a relatively large space for installation, the optical image stabilizer is hardly suitable for miniaturization of a monocular having a single erect prism in its telescopic optical system.
A telescopic observation optical instrument in the form of binoculars disclosed in published Japanese application No. 7(1995)-43645 (which is hereinafter referred to as Document III) comprises a pair of right and left variable apex angle prisms, each of which is disposed between an objective lens and an eyepiece lens of the respective telescopic optical system. It also has a vibration detector sensor for detecting vibrations of a body of the telescopic optical instrument, a pair of actuators for actuating the variable apex angle prisms, respectively, and a control circuit for determining the amount of motion according to the detected vibration.
Binoculars with a function of compensating for deteriorations of a telescopic optical image, such as image-shaking, is disclosed in published Japanese application No. 10(1998)-20213 (which is hereinafter referred to as Document IV). This apparatus comprises a pair of right and left correction lens, each disposed between an objective lens and an eyepiece lens of each of a pair of right and left telescopic optical systems, a vibration detector sensor for detecting vibrations of a body of the binoculars, an actuator for actuating the correction lenses at once and a control circuit for determining the amount of motion according to the detected vibrations.
The optical image stabilizers disclosed in Document I or II has the advantage of covering a wide range of practical application and, however, has limits to miniaturization and weight saving. Further, the optical image stabilizers disclosed in Document III or IV has the advantage of being rendered small in mechanism and, however, is disadvantageously limited in availability because of a small range of correctable vibrations.